Simulation and Analysis of High-Speed Droplet Spray Dynamics

Abstract

An experimentally validated computer simulation model has been developed for the analysis of gas-phase and droplet characteristics of isothermal sprays generated by pressure jet atomizers. Employing a coupled Euler-Lagrange approach for the gas-droplet flow, secondary droplet breakup (based on the ETAB model), was assumed to be dominant and the k-ε model was selected for simulating the gas flow. Specifically, transient spray formation in terms of turbulent gas flow as well as droplet velocities and size distributions are provided for different back pressures. Clearly, two-way coupling of the phases is important because of the impact of significant gas entrainment, droplet momentum transfer, and turbulent dispersion. Several spray phenomena are discussed in light of low back-pressure (1atm) and high back-pressure (30atm) environments. At low back-pressure, sprays have long thin geometric features and penetrate faster and deeper than at high back-pressures because of the measurable change in air density and hence drag force. Away from the nozzle exit under relatively high back pressures, there is no distinct droplet size difference between peripheral and core regions because of the high droplet Weber numbers, leading to very small droplets which move randomly. In contrast to transient spray developments, under steady-state conditions droplets are subject to smaller drag forces due to the fully-developed gas entrainment velocities which reduce gas-liquid slip. Turbulent dispersion influences droplet trajectories significantly because of the impact of random gas-phase fluctuations.

Effect of viscosity and surface tension on breakup and coalescence of bicomponent sprays

“…Experimental studies in swirling flows have reported contradictory results over the last few years (Shi and Kleinstreuer, 2007). More fundamental experimental works were conducted using optical diagnostics with water as the main fluid at different pressures (Saha et al, 2012;Davanlou et al, 2013).…”

Mechanisms of Pharmaceutical Aerosol Deposition in the Respiratory Tract

“…In the first phase, the instability of the jet coming from the nozzle forms primary droplets. In the second phase, the formation of the smaller secondary droplets is due to deformation of the primary droplets (61). Using the couple Euler-Lagrange approach for the gas droplet flow and an Enhanced Taylor Analogy Breakup model assuming the primarily droplet diameter equal to the nozzle diameter, Shi and Kleinstreuer were able to numerically simulate the droplet spray dynamics of several fluids including the droplet size and plume velocity as a function of distance from the nozzle exit (61).…”

A two-fluid model of gas-assisted atomization including flow through the nozzle, phase inversion, and spray dispersion

“…There are some variations between different authors regarding the classifications of the modes, e.g. Kolev (2002b), Lee and Reitz (2001), Shi and Kleinstreuer (2007); however, the general features of the break-up do not change. In this paper we will use Kolev (2002b) classification.…”

“…Even though the original model did not consider secondary break-up, coalescence, and size variations of droplets, it can be generalized to include these phenomena, e.g. Shi and Kleinstreuer (2007). The Eulerian description of the spray as a continuum is also possible, but it is not very popular in the spray-only computations.…”